Embodiments of the disclosed technology relates to a PDLC film structure, a manufacturing method and a controlling method thereof.
Polymer-dispersed liquid crystal (PDLC) is a kind of material which has a polymer matrix with liquid crystal micron droplets uniformly dispersed therein and is obtained by a polymerization reaction after low-molecular liquid crystal is mixed with a prepolymer. This material can achieve an electro-optical response characteristic by using the anisotropy of the liquid crystal molecules without requiring a polarization board and an alignment layer. A PDLC film largely depends on the match between the effective refractive index of the liquid crystal molecules and the polymer matrix.
When a conventional PDLC film prepared with positive liquid crystals is not applied with a voltage, the liquid crystal molecules are randomly oriented, so that the incident light is repeatedly refracted and reflected at the interfaces between the liquid crystal molecules and the polymer matrix, thereby exhibiting a milky scattering state. When a voltage is applied, the liquid crystal molecules are arranged along the direction of the electric field, so that the incident light is not refracted and reflected but is transmitted out.
Typically, a ratio of the amount of the transmitted light corresponding to the liquid crystal molecules in the current positions to the amount of the transmitted light corresponding to the liquid crystal molecules in the final positions is called a transmittance. The time required by changing a 10% transmittance to a 90% transmittance when the liquid crystal device is turned on is called a rise time, and the time required by changing a 90% transmittance to a 10% transmittance when the liquid crystal device is turned off is called a fall time, and the total response time of the liquid crystal is the sum of both. For a PDLC film, the impact on its response time has many factors, which not only relates to polymeric material selection, concentration ratio before the polymerization, and the polymerization process conditions, but also relates to shape, frequency, amplitude of the driving pulse during normal working of the resultant film, thus, to some extent, resulting in a variety of materials with different response times of long or short. But fundamentally speaking, the response time of a PDLC film is determined by an anchoring energy of polymer matrix on the liquid crystal molecules and the intensity of the electric field where the liquid crystal is located. In general, in case of a lower anchoring energy of the polymer matrix on the liquid crystal molecules, there is a contradictory relationship in which the PDLC film has a short rise time but a long fall time (and vice versa).
In the related art, the commonly used PDLC film has a larger liquid crystal ratio with a larger liquid crystal mesh, which in turn leads to a lower anchoring energy of the polymer matrix on the liquid crystal molecules in the PDLC film. That is, the PDLC film has a short rise time but a long fall time, i.e., when a voltage is applied to the PDLC film, the liquid crystal molecules rotate to the electric field direction faster, but when the voltage application is stopped, the liquid crystal molecules are returned from the electric field direction to the state before application of voltage slowly.